FPS downgrade going to 7850 2gb from 550 ti

My GF just moved up to 25 man raiding and it started to add noticeable FPS slowdowns with the GT 240 she was using. I bought a Power color 7850 2GB and threw my old 550 TI in her computer. Her FPS improvement is noticeable and runs fine at 1680x1050.

I've always played at 1920x1080 on a Phenom II 965 BE using that 550 ti with 8GB RAM. I play on decently high settings with some stuff I don't care about turned down like shadows, texture filtering, and SSAO. I do play Windowed Fullscreen since I run two monitors and it's easier to move over to the desktop this way.

TLDR: Kept everything the same, installed a more powerful card and my FPS is down ~20 FPS. I've tried old drivers, new drivers, beta drivers. Removing every old display driver with Driver Fusion and reinstalling again. Tried OC'd 7850 and back to stock again. This card just really isn't doing much in WoW.

I don't play any other games so I don't need a more powerful card, I assumed this card should be more than enough for WoW.

I know many people have had problems with 7850 and WoW, including tomshardware initial benchmarks crashing many times after starting WoW. Any solutions that I haven't tried yet?

Returning it and getting another nvidia card is also an option, in the ~$200 range is that a better solution?

For future reference. If you solely play video games from Blizzard (WoW, Diablo, SC2) the GTX660 is the best value for money card available. The 7850 is a great card as well but the GTX660 is quite a bit better.